More than 100 Northwestern University students watched as a naked 25-year-old woman was penetrated by a sex toy wielded by her fiancee during an after-class session of the school’s popular “Human Sexuality” class.

The woman said she showed up at the Feb. 21 lecture in the Ryan Family Auditorium in Evanston expecting just to answer questions, but was game to demonstrate. The course’s professor on Wednesday acknowledged some initial hesitation, but said student feedback was “uniformly positive.”

The p.r. flack for Northwestern defended the “lecture” and “demonstration” as an example of teaching that puts the high-priced school “at the leading edge.”

At least one student who witnessed the XXX-rated demo had a more accurate description:

“I didn’t expect to see a live sex show,” said Justin Smith, 21, a senior economics and political science major who was in the after-class session. “We were told we were going to have some people talk to us about the fetish world and kink.”

…After the demonstration, several students tried a different sex toy that gave a “titillating” but not painful shock, testing it out on their arms, said Ken Melvoin-Berg, who narrated the after-class lecture. Melvoin-Berg said the school paid him between $300 to $500 for his appearance.

Faith Kroll, the woman who stripped, was laying down on a towel when she was penetrated. When she arrived, she thought she just would be answering students’ questions and showing off sex toys they brought, including whips, paddles and a clown wig.

…Melvoin-Berg said he met Prof. Bailey through a swinging couple who previously spoke to the class. Melvoin-Berg runs the “Weird Chicago Red Light District Sex Tour,” which has participants playing games like “spot the ho” as they travel the city looking for prostitutes. He also teaches “Networking for Kinky People,” a 3-hour version of the one hour lecture he gave at Northwestern.

Melvoin-Berg said the sex toy used was BDSM, but was “not like a pain thing…we wanted to make it poignant.”

“I did mention this was going to be the best money their parents had spent on their education,” he said.

What’s next? A guest lecture with Charlie Sheen and his goddesses?

I bet a few of the parents of these students wouldn’t mind taking a paddle to the clowns running this university-turned-S&M theater…